The present invention relates to a head-up display suited for mounting on vehicles such as cars and vessels.
To provide navigation information or the like for a car driver (observer), there is used a head-up display comprising a combiner to be arranged in front of the observer and a display element which projects image displaying light from its image displaying face. By changing the optical path of the image displaying light by the combiner, a virtual image, that is a subject of observation, is formed in front of the combiner. A landscape in front of the combiner can be visually recognized by the light which passes through the combiner.
When the optical path of the image displaying light from the display element is changed directly by the combiner, the distance from the observer to the position, at where the virtual image is formed, shortens, because the optical path of the image displaying light between the display element and the observer""s pupil shortens. This extends the time required to change the observer""s condition from watching the actual landscape in front of the car to recognizing the virtual image. This is undesirable for vehicle driving. When the distance between the display element and the combiner is increased to lengthen the optical path of the image displaying light from the display element to the observer""s pupil, the problem of increased size of the head-up display is generated.
To resolve this problem, a mirror facing the image displaying face can be provided. By introducing image displaying light to the combiner by reflecting the image displaying light by the mirror""s reflecting surface, the optical path of the image displaying light can be lengthened in a given space without increasing the size of the head-up display.
However, the reflecting surfaces of the conventional mirrors are flat or concave. Therefore, the external light, such as solar light, which passes through the combiner, is focused in a narrow range on the image displaying face by being reflected by the mirror. The infrared rays contained in the external light are then absorbed in the image displaying face, resulting in heat concentration on the image displaying face and hence the problems of displaying performance reduction etc are generated.
The object of the present invention is to provide a head-up display free of the above-described problems.
The present invention relates to a head-up display comprising a combiner to be arranged in front of an observer; and a display element which projects image displaying light from its image displaying face; wherein a virtual image, that is a subject of observation, is formed in front of the combiner by changing the optical path of the image displaying light by the combiner; and wherein an optical component facing the image displaying face is provided so that the image displaying light can be introduced to the combiner by changing the optical path of the image displaying light.
The present invention is characterized in that the optical component is capable of diverging incident light.
According to the constitution of the present invention, the external light, such as solar light, which passes through the combiner, is diverged on the optical path changing face of the optical component. Therefore, the external light does not focus in a narrow range, so that heat concentration on the image displaying face by the infrared rays contained in the external light is mitigated.
In the head-up display of the present invention, it is preferable that the optical path changing face of the optical component is arranged so as to be inclined with respect to the vertical direction to allow the image displaying light to ascend as the light goes forward by changing the optical path; and that the image displaying face is arranged so as to be inclined with respect to the vertical direction to allow itself to depart from the optical component as it descends.
By this constitution, the external light, such as solar light, which passes through the combiner, can be prevented from going toward the observer after its optical path is changed on the image displaying face.
In the head-up display of the present invention, it is preferable that the optical path changing face of the optical component change the optical path of the external light, which passes through the combiner, so that the external light does not again go to the combiner.
By this constitution, the external light can be prevented from reaching the observer""s pupil.
According to the present invention, a head-up display of good visibility, which can reduce the amount of infrared rays contained in the external light absorbed in the image displaying face and can prevent the displaying performance reduction, can be provided.
In the head-up display of the present invention, it is preferable that the optical path of the image displaying light, which is projected from any one point of the display element, from the optical component to the combiner is located above the optical path of the image displaying light from the projection point to the optical component and also below the optical path of the image displaying light from the combiner to the observer""s pupil.
By this constitution, the display element can be placed as close to the combiner as possible. Therefore, the head-up display can be made more compact, so that it is suited for installation in the narrow space inside a car compartment.
In the head-up display of the present invention, it is preferable that the combiner comprises a body, and a reflecting layer which covers one face of the body, that at least one side of the body is configured with a platy material made of synthetic resin, that the platy material is covered with a coating which is harder and smaller in thermal expansion coefficient than the platy material, that the reflecting layer is formed on the coating, that the reflecting layer is configured with a plurality of laminated films, which are smaller in thermal expansion coefficient than the platy material and have mutually different refractive indexes, and that each of the films has residual compressive stress at normal temperature.
According to the above-described constitution, the deterioration of the combiner due to swelling and solar light exposure can be prevented by covering the platy material of synthetic resin constituting the body by a coating which is harder and smaller in thermal expansion coefficient than the platy material. Because the reflecting layer, which is configured with a plurality of films, is formed on the coating, the reflecting layer can be prevented from cracking and peeling from the body. Thereby, the combiner is of high reflectance and high transparency. Moreover, because each of the films constituting the reflecting layer has residual compressive stress at normal temperature, internal tensile stress can be prevented from being exerted on the reflecting layer, even if the body is expanded, whereby the reflecting layer can be prevented from peeling and cracking.
In the head-up display of the present invention, it is preferable that the image displaying light is projected from a liquid crystal display element having a backlight device, that the light source for backlight of the liquid crystal display device has a fluorescent tube, a driving circuit for the fluorescent tube, a lead which connects the fluorescent tube to the driving circuit, and a support portion, that the light source for backlight is made as a unit attachable to, and detachable from a housing which houses the liquid crystal display element, that the fluorescent tube is supported by the support portion so that it is arranged in a space outside the support portion, that the driving circuit and the lead are arranged in a space inside the support portion, and that the outer surface of the support portion serves as a backlight reflecting surface which reflects the light beam for backlight generated by the fluorescent tube.
According to this constitution, replacement of the bulb of a damaged or expiring fluorescent tube is facilitated by removing the light source for backlight from the housing.
Because the above-described driving circuit and lead are arranged in the space inside the support portion, they are shielded against water droplets, foreign substances, etc., and prevented from damaging.
Because the fluorescent tube is supported by the support portion and because the outer surface of the support portion constitutes the backlight reflecting surface, the driving circuit can be placed as close to the fluorescent tube as possible, whereby the light source for backlight can be made more compact. Also, because the lead which connects the driving circuit and the fluorescent tube can be shortened, startability reduction can be prevented.
Preferably, at least the outer surface of the support portion is configured with a shielding material capable of shielding electromagnetic waves, and the shielding material constitutes the backlight reflecting surface. By this constitution, the noise from the driving circuit can be prevented from affecting surrounding electronic instruments to improve EMI performance.
In the head-up display of the present invention, it is preferable that the image displaying light is projected from a liquid crystal display element, and that the display element has a transmission type monochromatic simple matrix liquid crystal display device whose liquid crystal action mode is the BTN mode, a backlight device capable of changing the light emission wavelength peak of the light which irradiates the liquid crystal display device, and a controller which synchronizes the image displaying timing on the liquid crystal display device and the light emission timing at the desired light emission wavelength peak in the backlight device.
According to this constitution, when a plurality of images constituting one information are repeatedly displayed on a time sharing basis by the liquid crystal display device, the displaying timing for each image and the light emission timing at the desired light emission wavelength peak in the backlight device can be synchronized. Therefore, the observer can realize the one information as a multiple-colored image without using a color filter. Also, because the liquid crystal action mode of the liquid crystal display device is the known BTN mode, quick image switching is possible without using a switching component, such as TFT. Therefore, a plurality of images can be displayed on a time sharing basis.
In the head-up display of the present invention, it is preferable that one of the housing and the combiner is provided with an insertion portion, that the other of the housing and the combiner is provided with a pit into which the insertion portion is extractably inserted, and that the combiner is supported by the housing via the insertion portion and the pit.
According to this constitution, the stress based on the bending moment etc. generated by the external force exerted on the combiner acts on the housing via the insertion portion and the pit. The stress is therefore dispersed over the entire contact range of the insertion portion and the pit. Therefore, the space inside the housing can be increased to facilitate parts arrangement in the housing, because it is unnecessary to thicken the housing to improve its strength. Also, the combiner can be separated from the housing by extracting the insertion portion from the pit, whereby cleaning and other maintenance work for the combiner are facilitated.
Preferably, the contact portions of the insertion portion and the pit are curved so that the normal direction of the optical path changing face of the combiner changes as the depth of insertion of the pit into the insertion portion changes. Alternatively, the outer face of the insertion portion and the inner face of the pit are formed along a cylindrical face so that the normal direction of the optical path changing face of the combiner changes as the insertion portion rotates relative to the pit.
By this constitution, the position of the combiner relative to the housing can be changed when the combiner is supported by the housing via the insertion portion and the pit.
Preferably, the insertion portion is capable of exerting an elastic force on the pit, and the position of the insertion portion relative to the pit can be retained by the frictional force generated by the elastic force. Alternatively, it is preferable that one of the insertion portion and the pit is provided with a plurality of grooves along the direction of insertion of the insertion portion into the pit, that a retention element having a projection, which can be fitted into each groove, is attachable to, and detachable from the other of the housing and the combiner, and that the projection is fitted into any one of the grooves to retain the position of the insertion portion relative to the pit.
By this constitution, the position of the virtual image, that is the subject of observation, can be finely adjusted because the position of the combiner relative to the housing can be finely adjusted.